Many types of devices are used to provide filtered air by removing unwanted particles from the surrounding environment. For example, air purifiers, and central heating, ventilation and air-conditioning (HVAC) systems can be used to provide filtered air in a home environment. Many devices require filtered air to protect internal components from abrasion and/or corrosion due to the intake of foreign particles. For example, computers, and industrial equipment enclosures and control panels require filtered air to protect internal components.
A conventional air filter is typically mounted in a frame for easy insertion of the filter into (or onto) a filter housing of a device that circulates air through the air filter. The designs of the frames and housings typically involve mechanical means for holding the filter in place. Frames typically are made of molded polymer or folded cardboard. Housings typically include clamps, friction fit, snap fit, sliding mount, elastic straps, etc. The size of these frame/filter assemblies is not easily modified by the consumer. Thus, it is difficult to customize the filter member and a large inventory is required for different sizes. Therefore, there exists a need for a filter that is easily customized. Also, there exists a need for an inexpensive, bulk filter media that is readily adaptable to a wide range of applications simply by cutting to shape by the consumer.
A filter can also be adhesively mounted. Such mounting means have included double-coated tapes, for example, which have been used around the periphery of a filter. Effective anchoring of a filter with a peripheral adhesive attachment means typically requires that the filter be precut to the shape required by the target appliance so that the adhesive contacts a suitable anchoring site on the appliance. Unfortunately, these adhesive mounting means do not provide advantage for a wide variety of applications, nor are they easy to use for a wide variety of applications. Also, U.S. Pat. No. 5,912,369 (Reeves) discloses the use of a layer of an adhesive coating on one entire face of a fibrous air filter member. This approach requires the coating weight of the adhesive to be carefully controlled so as to minimize the air flow pressure drop while achieving the desired adhesive strength. U.S. Pat. No. 5,912,369 (Reeves) also discloses a spray-coated adhesive was vacuumed into the fibrous interstices of the filter material, and a second light spray-coated adhesive was then applied to the filter material, the two adhesive coatings acting together to retain the filter material onto a target surface (i.e. an appliance housing). Such spray application would typically not provide a substantially continuous adhesive-rich region in the fibrous filter media because a spray-coated adhesive typically produces only a thin adhesive, typically discontinuous coating on individual fibers.
A number of disadvantages exist with conventional adhesively mounted filters. For example, for those assemblies with adhesive on an entire face of the filter member, the filtration effectiveness may be unsuitable for many applications due to the resulting high pressure drop of the filter. For those assemblies with adhesive at the periphery of a filter, exact placement of the filter is not very easy and improper placement can result in poor adhesion or anchoring to the appliance. Also, if an aggressive adhesive is used or if filter media integrity is not sufficiently strong, filter removal can be difficult, often times resulting in adhesive and/or filter member residue being left on the target surface.
The present invention provides filter assemblies with adhesive attachment systems. The adhesive attachment system is more versatile (for both the filter manufacturer and the consumer) than conventional systems and provides a greater ability to reduce, and preferably eliminate, residue on the device upon removal of the filter assembly.
In one embodiment, a filter assembly includes a porous filter member and an adhesive disposed on a reinforcement scrim adhesively attached to at least a portion of at least one major surface of the porous filter member, wherein the reinforcement scrim has discrete open areas.
In an alternative embodiment, a filter assembly includes a porous filter member that includes a fibrous filter member and an adhesive impregnated into discrete areas of the porous filter member such that there is a substantially continuous adhesive region throughout at least about 25% of the thickness of the porous filter member in the discrete regions.
For the embodiment with the reinforcement scrim, the discrete open areas of the scrim preferably have an average effective circular diameter of at least about 300 microns. It can be formed from a variety of materials, preferably it is formed from a thermoplastic polymer, such as a polyolefin (e.g., a polypropylene polymer). As used herein, a polymer includes within its scope homopolymer and copolymer, and copolymer refers to polymers prepared from two or more different monomers (e.g., terpolymer, tetrapolymer). Also, as used herein, xe2x80x9caxe2x80x9d or xe2x80x9canxe2x80x9d refers to one or more, thereby encompassing more than one element, whether it be a layer, a fiber, a polymer, etc., in a construction.
The scrim can be adhesively attached to the entire surface of at least one major surface of the porous filter member, or it can be adhesively attached to discrete regions, such as the periphery, of at least one major surface of the porous filter member.
The filter member can include a fibrous nonwoven web, a foam, or a porous membrane. Typically, a fibrous nonwoven web is used. It preferably includes electret fibers, which may be split fibers, spunbond fibers, tribocharged fibers, melt blown fibers, etc. The filter member can also include additional components, such as absorptive or adsorptive particles.
The adhesive is preferably a pressure sensitive adhesive, such as a (meth)acrylic-based adhesive, a poly(alpha-olefin)-based adhesive, a synthetic rubber-based adhesive, or a silicone-based adhesive.